Conventionally, an inkjet head which uses the piezoelectric effect of a piezoelectric element for recording has been known.
This inkjet head has a piezoelectric actuator. The piezoelectric actuator includes a common electrode, a piezoelectric element and an individual electrode, which are formed in this order into a layered structure. A diaphragm is formed over a surface of the piezoelectric actuator. The diaphragm is adhered onto an ink passage member with an adhesive to form a pressure chamber. In order to eject ink, the voltage is applied to the common electrode and the individual electrode, so that the piezoelectric element expands or shrinks. The expansion/shrinkage is constrained by the diaphragm, whereby the piezoelectric actuator deflects in the thickness direction. The deflection causes a change in the volume of the pressure chamber, so that the ink in the pressure chamber is ejected from a nozzle.
However, in a production process of the piezoelectric actuator, at the step of forming a piezoelectric element on an electrode, foreign substance adhered when the electrode is formed by sputtering is, for example, introduced into the piezoelectric element, whereby a defective portion is generated in the piezoelectric element in some cases. Due to the defective portion, the voltage-withstanding characteristics of the piezoelectric element deteriorate, so that there is a possibility that dielectric breakdown is caused in an ink ejection operation.
In a technique disclosed in Japanese Unexamined Patent Publication No. 2000-351212, an insulating material is applied onto a piezoelectric element using a spin coater such that a defective portion is filled with the insulating material, and an insulating layer is formed on the piezoelectric element. Then, the insulating layer is removed by dry etching in order to prevent the deterioration of the piezoelectric characteristics. As a result, the voltage-withstanding characteristics of the piezoelectric element are improved, and dielectric breakdown is prevented.
However, removing only the insulating layer by dry etching is not an easy task. Furthermore, because of the difficult task of removing the insulating layer, the production yield is decreased, and the production cost is increased.
The present invention was conceived in view of the above problems. An objective of the present invention is to improve the piezoelectric characteristics and voltage-withstanding characteristics of a piezoelectric element without removing an insulating layer formed on the piezoelectric element.